1. Field of the Invention
The present invention relates to a Light Emitting Diode (LED) driving apparatus applicable to a Liquid Crystal Display (LCD) backlight unit, and more particularly, to an LED driving apparatus having a temperature compensation function, which can compensate luminance variation according to temperature changes by using a forward voltage of an LED light source so that the forward voltage of the LED light source is controlled in association with a target current value of ambient temperature, without having to use an optical sensor or temperature sensor or memory or judging means such as CPU, thereby decreasing an installation space, saving manufacturing costs and promoting design flexibility.
2. Description of the Related Art
According to characteristics of LEDs used in an LCD backlight or lighting instrument, their junction resistance is generally variable according to temperature. Therefore, an LED drive apparatus is required to have temperature compensation means.
FIG. 1 is a block diagram of a conventional LED driving unit.
Referring to FIG. 1, the conventional LED driving unit includes a control unit 10 for performing operation control via supply voltage Vcc and feedback voltage Vfd, a driving unit 20 for supplying the supply voltage Vcc in response to the control of the control unit 10, a LED light source 30 including a plurality of LEDs which emit light in response to the supply voltage of the driver 20, an optical sensor 40 for detecting light emitted from the LEDs and a feedback circuit 50 for supplying the feedback voltage Vfd in response to a detection signal by the optical sensor 40 to the control unit 10.
The driving unit 20 is composed of a transistor Q1 that adjusts the supply voltage in response to a supply control signal from the control unit 10.
In the conventional LED driving apparatus, the feedback circuit 50 compares the detection signal by the optical sensor 40 with a reference signal to supply the feedback voltage Vfd, corresponding to an error signal of the comparison result, to the control unit 10. In this case, the control unit 10 varies the supply voltage in response to the feedback voltage Vfd to control the operation of the LEDs.
Such a conventional LED driving apparatus uses an automatic power control process.
For example, when LED light quantity is reduced according to some reasons such as rise in external temperature, monitoring current of PD is also lowered and the comparison result in relation with the reference voltage is fed back proportionally. In this case, the control unit controls the operation in response to the feedback voltage in such a fashion of increasing the collector current of the transistor Q1 of the driving unit so that light quantity can be maintained constantly.
However, the conventional LED driving apparatus uses an expensive photo-sensor or optical sensor for directly monitoring the light quantity of the LEDs. The expensive optical sensor becomes burdensome for a low cost assembly product, which is provided as a set. Furthermore, in case of using RGB LEDs, monitoring necessary for respective wavelengths disadvantageously increases cost burden.